Stabilization of aqueous solutions of certain acid substituted spectral sensitizing dyes

ABSTRACT

AQUEOUS SOLUTIONS OF ACID SUBSTITUTED PHOTOGRAPHIC SPECTRAL SENSITIZING DYES HAVING A PH OF ABOUT 6 TO 7.5 ARE PROVIDED, SAID SOLUTIONS EXHIBITING EXCELLENT STABILITY AGAINST LOSS OF DENSITY DURING STORAGE IN COMPARISON TO SIMILAR AQUEOUS DYE SOLUTIONS HAVING A HIGHER OR LOWER PH.

United States Patent O1 US. Cl. 260-240.65 5 Claims ABSTRACT OF THE DISCLOSURE Aqueous solutions of acid substituted photographic spectral sensitizing dyes having a pH of about 6 to 7.5 are provided, said solutions exhibiting excellent stability against loss of density during storage in comparison to similar aqueous dye solutions having a higher or lower pH.

This application is a division of our copending application Ser. No. 521,529, filed Jan. 19, 1966, now abandoned in favor of the instant divisional application and continuing application Ser. No. 830,482, filed June 4, 1969.

This invention relates to novel photographic materials, and to processes for preparing photosensitive compositions.

One aspect of the invention relates to improved processes for spectrally sensitizing photographic emulsions. The invention also relates to novel solutions of spectral sensitizing dyes.

It is especially desirable to spectrally sensitize photosensitive materials dispersed in a hydrophilic colloid with aqueous solutions of spectral sensitizing dyes. Aqueous dye solutions may be added to hydrophilic colloid systems conveniently, thereby avoiding the problems encountered when organic solvent solutions of dyes are employed. One of the principal disadvantages of using organic solvent solutions of sensitizing dyes is that coating defects frequently occur when the hydrophilic colloid system is coated on a support.

One of the problems with aqueous solutions of watersoluble acid substituted dyes has been the tendency of the dye to lose density rapidly during storage. This characteristic is quite objectionable in manufacturing operations where it is desirable to prepare the dye solution considerably before it is incorporated in the photosensitive material. We have now found a method for increasing the stability of aqueous solutions of acid substituted dyes against loss of density during storage.

One object of this invention is to provide novel aqueous solutions of spectral sensitizing dyes which are stabilized against loss of density during storage. Another object of this invention is to provide a novel process for spectrally sensitizing photosensitive materials dispersed in a hydrophilic colloid with stabilized solutions of spectral sensitizing dyes. Still another object of this invention is to provide novel aqueous solutions of acid substituted spectral sensitizing dyes which do not decompose even when exposed to light for considerable periods of time. Other objects of this invention will be apparent from the following disclosure and appended claims.

In one embodiment of this invention, we provide novel aqueous solutions of acid substituted spectral sensitizing dyes having a pH between 6 to 7.5. We have found that such solutions of spectral sensitizing dyes exhibit excellent stability against loss of density during storage. It has further been found that the dye solutions in accordance with this invention unexpectedly fail to decompose ice even upon exposure to light for considerable periods of time.

In another embodiment of this invention, aqueous solutions of acid substituted spectral sensitizing dyes maintained at a pH of about 6 to 7.5, are added to photosensitive materials, such as silver halide, dispersed in a hydrophilic colloid.

Any suitable base may be employed to adjust the pH of the dye solutions in accordance with the invention. Preferably, weak organic bases are used, such as pyridine, isoquinoline, quinoline, and 2,6-dimethylpyridine. Especially good results are obtained with nitrogen-containing weak organic bases. Stronger bases, such as inorganic bases (eg. NaOH) can be employed although it is sometimes more diflicult to achieve the proper pH therewith. Preferably, the pH of the solution is adjusted soon after the dye is dissolved. It is, of course, desirable to adjust the pH prior to any substantial loss of dye density.

In the preferred embodiments of the invention, water is the sole solvent. However, minor proportions (e.g. up to about 45%) of organic solvents may be used if desired. With some dyes it is necessary to use minor portions of organic solvent, such as an alcohol, e.g., methanol, ethanol or propanol, or other organic solvents such as acetone.

The invention is especially useful with the acid substituted spectral sensitizing dyes, such as the acid substituted cyanine or merocyanine dyes. Preferably, to impart greater water solubility, the dyes are diacid substituted. Typical acid substituents are sulfato, sulfo and carboxy groups, such as the sulfoalkyl and carboxyalkyl groups wherein the alkyl substituent has from 1 to 4 carbon atoms. Typical useful dyes are all those disclosed in US. Pats. 2,503,776; 2,526,632; and 3,148,187. The invention is particularly useful with the diacid substituted oxacarbocyanine dyes, which exhibit a pronounced tendency to decompose rapidly in aqueous solutions.

Especially useful dyes herein include the nuclear sulfosubstituted cyanine dyes represented by the formula:

in which R and R each represents a lower alkyl group such as methyl, ethyl, propyl, isopropyl, butyl, secondary butyl, tertiary butyl, etc., a sulfoalkyl group in which the alkyl group has from 1 to 4 carbon atoms, such as sulfomethyl, sulfoethyl, sulfopropyl, snlfobutyl, etc., and a carboxyalkyl group in which the alkyl group has from 1 to 4 carbon atoms such at carboxymethyl, carboxyethyl, carboxypropyl, carboxybutyl, etc.; R represents a hydrogen atom or a lower alkyl group such as methyl, ethyl, propyl, butyl, etc.; Z and Z each represents the nonmetallic atoms necessary to complete a heterocyclic nucleus of the benzothiazole series (e.g., benzothiazole, 4-chlorobenzothiazole, 5-chlorobenzothiazole, 7-chlorobenzothiazole, 4-methylbenzothiazole, S-methylbenzothiazole, S-bromobenzothiazole, 4-phenylbenzothiazole, 5- phenylbenzothiazole, 6-phenylbenzothiazole, 4-methoxybenzothiazole, S-methoxybenzothiazole, 5-iodobenzothiazole, 4-ethoxybenzothiazole, S-ethoxybenzothiazole, =5- hydroxybenzothiazole, etc.); those of the naphthothiazole series (e.g., (it-naphthothiazole, t l-naphthothiazole, S-methoxy-fl-naphthothiazole, 5-ethyl-fi-naphthothiazole, 8- methoxy-a-naphthothiazole, 7-methoXy-wnaphthothiazole, etc.); those of the benzoxazole series (e.g., benzoxazole, S-chlorobenzoxazole, S-methylbenzoxazole, S-phenylbenzoxazole, S-methoxybenzox-azole, S-ethoxybenzox-azole, 5- hydroxybenzoxazole, etc); those of the naphthoxazole series (e.g., (it-naphthoxazole, fl-naphthoxazole, etc.); those of the benzoselenazole series (e.g., benzoselenazole, 5-

chlorobenzoselenazole, S-methylbenzoselenazole, S-hydroxybenzoselenazole, etc.); those of the naphthoselenazole series (e.g., a-naphthoselenazole, fi-naphthoselenazole, etc.); those of the quinoline series including the 2-quinolines (e.g., quinoline, 3-methylquinoline, S-methylquinoline, 7-methylquinoline, 8-methylquinoline, 6-chloroquinoline, 8-chloroquinoline, 6-methoxyquinoline, 6-hydroxyquinoline, 8-hydroxyquinoline, etc.); the 4-quinolines (e.g,. quinoline, 6-methoxyquinoline, 7-methoxyquinoline, 8- methoxyquinoline, etc.); those of the isoquinoline series (e.g., the l-isoquinolines, the 3-isoquinolines, etc.); at least one of the groups Z and Z having a sulfo-substituent; and n is the integer l, 2 or 3.

Another useful class of dyes in this invention includes those having the formula:

wherein R, Z and Z have the meanings given above; L represents a methine group (e.g., CH=, C(CH etc.); and D represents a divalent hydrocarbon radical, e.g. methylene, ethylene,

trimethylene, etc. In this formula, neither Z nor Z is necessarily sulfo-substituted.

The invention may also be practised with dyes having the following general formula:

Q1 d-l wherein R and R each represents an alkyl group (substituted or unsubstituted), e.g. methyl, ethyl, n-butyl, isobutyl, allyl, Bethoxyethyl, fl-hydroxyethyl, fl-acetoxyethyl, carbethoxymethyl, benzyl, fi-phenylethyl, etc. ,(e.g. an alkyl group, especially a primary alkyl group, containing from 1 to 8 carbon atoms), or an aryl group, e.g. a monocyclic aryl group of the benzene series, such as phenyl, p-chlorophenyl, etc., L represents a methine group (substituted or unsubstituted), n represents a positive integer from 1 to 2, m and d each represents a positive integer from 1 to 3, Q represents an oxygen atom, a sulfur atom, or a group of the formula wherein R represents an alkyl group (substituted or unsubstituted), e.g. methyl, ethyl, n-butyl, isobutyl, allyl, B-ethoxyethyl, B-hydroxyethyl, fl-acetoxyethyl, carbethoxymethyl, benzyl, fl-phenylethyl, etc. (e.g. an alkyl group, especially a primary alkyl group, containing from 1 to 8 carbon atoms), or an aryl group, e.g. a monocyclic aryl group of the benzene series, such as phenyl, p-chlorophenyl, etc., Q represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing atoms in the ring, e.g. a rhodanine nucleus, a 2-thio-2,4(3,5)- oxazoledione nucleus, a S-pyrazolone nucleus, a Z-thiohydantoin nucleus, etc., said heterocyclic nucleus containing at least one group selected from the group consisting of a monocyclic carboxyaryl group of the benzene series (e.g. a p-carboxyphenyl group, a 3-carboxy-4-hydroxyphenyl group, etc.) a carboxyaryl group of the naphthalene series (e.g. a 4-carboxy-l-naphthyl group, etc.); a monocyclic sulfoaryl group of the benzene series (e.g. a p-sulfophenyl group, a 2,5-disulfophenyl group, etc.), and a sulfoaryl group of the naphthalene series (e.g. a 4-sulfo-1-naphthyl group, etc.), and alkali metal (e.g. sodium, potassium, lithium, etc.) and ammonium salt forms of these groups, and Z has the meaning given above.

The effective concentrations of dye required to spectrally sensitize photosensitive materials are the same as 4 with prior art dye solutions. For example, in sensitizing silver halide, the most useful concentration of dye is from about 5 to about 100 mg. per liter of fiowable silver halide emulsion. The operable concentration may vary over a Wide range, if desired.

The most useful dyes have a solubility in 'water at the rate of at least .001 part in 5 parts aqueous solution. As used herein, aqueous solution includes solutions Where Water is the sole solvent as well as aqueous solutions containing minor portions of organic solvent as described above.

This invention will be further illustrated by the following examples.

Example 1 illustrates the excellent stability of dye solutions of the invention.

EXAMPLE 1 Dye I, anhydro-5,5'-dichloro 9 ethyl 3,3'-di(3- sulfopropyl)oxacarbocyanine hydroxide, sodium salt is dissolved at 0.3 g./100 ml. solution in 0.01 M and 0.001 M aqueous pyridine at room temperature using an ultrasonic generator, and stored in a glass-stoppered flask in the dark at about 36 F. for 17 days. Dye density and pH measurements after that time show essentially no difference from those of the freshly prepared solutions, as shown below.

Density pH at 493 mp 17 17 Solution Fresh days Fresh days 0.01 M aqueous pyridine plus Dye I 7. 2 7. 0 1. l6 1. 16 0.001Maqueouspyridine plus Dye I 6. 4 6. 25 1. 16 1.15

A sample of the dye solution which had been stored at 36 F. for 17 days was placed in a clear glass container and exposed to normal laboratory lighting at room temperature for an additional 60 days. There was no measurable decomposition of the dye at the end of this period. This is highly unexpected since most cyanine dyes decompose rapidly on exposure to light.

Example 2 illustrates the excellent sensitizing properties of dye solutions of the invention.

EXAMPLE 2 A green-sensitive layer of the type described in US. Pat. No. 3,046,129, spectrally sensitized with Dye I at 100 mg. per mole silver from the following solutions is coated on a cellulose acetate film support at 350 mg. silver per square foot and 810 mg. gelatin per square foot. The dried coatings are exposed and developed for 5 minutes in Kodak =DK-50 Developer and fixed, washed and dried with the following results.

Rel; Dye I solution speed Fog 5 mg./6 cc. MeOH 100 04 5 mg./3 cc. MeOH 04 3 mg./1 00. .001 M aqueous pyridine 91 04 The small difference in relative speed is of negligible significance in practice.

EXAMPLES 3-12 Aqueous solutions of various spectral sensitizing dyes are prepared as described in Example 1.

Example 7.4 (3 ethyl 2(3)-benzothiazolylidene)-3- methyl-l (p-sulfophenyl) -5-pyrazolone.

Example 8.3-(p carboxyphenyl) 5 (3-methyl-2(3) benzoxazolylidene)-rhodanine.

Example 9.5 [(3 ethyl 2(3)-benzoxazolylidene) ethylidene] 3 (p sulfophenyl)2-thio-2,4(3,5)-oxazoledione.

Example 10.Anhydro 3 [3 carboxyethyl-5,5'-dichloro 9 methyl 3' ,B-sulfoethylthiacarbocyanine hydroxide.

Example 11.Anhydro 5,5 dichloro 9 ethyl-3,3-

di-B-sulfoethylthiacarbocyanine hydroxide.

Example l2.-Anhydro 5,5 dichloro-3,3' di-p-sulfobenzylthiacarbocyanine hydroxide.

In Examples 7-9, the aqueous solutions contain minor proportions of ethanol to provide a sufliciently high concentration of the sensitizing dye in the solution. The solutions obtained in Examples 3-12 all exhibit greatly increased stability to loss of density during storage when compared to control solutions which do not have the pH regulated in accordance with this invention. Each of the dyes of these examples, when used to sensitize emulsions as described in Example 2, provide excellent spectral sensitization. The spectral sensitization is essentially the same as that obtained when control solutions of the dyes, which are not regulated to a pH in accordanc with the invention, are used to sensitize the emulsion.

The necessity for controlling the pH of the aqueous dye solutions in accordance with the invention is illustrated by Example 13.

EXAMPLE 13 Densities at 493 My Aqueous solutions of Dye I Fresh 1-3 days p 5-21 days Control (water only) 1. 16 94 8 Water and 2 ml. acetic acid. 73 Water and 2 ml. triethylarnino 69 Water and 1 ml. acetic acid and 1 m1.

triethylarnine 1. 12 96 16 It may be seen that solutions of dyes which have a pH outside the range of the invention have poor stability.

The aqueous solutions of sensitizing dyes in accordance with the invention may be prepared by dissolving the dye in the aqueous solution at elevated temperatures or, by subjecting the mixture of dye and aqueous solution to ultrasonic agitation. The latter process allows relatively low temperature dissolving of the dye, thereby avoiding danger of damaging the sensitizing qualities of the dye.

The highly stable aqueous dye solutions of this invention may be employed to spectrally sensitize a wide variety of photographic materials including zinc oxide, titanium dioxide, organic photoconductors and silver halide, such as silver chloride, silver bromide and mixed halides such as silver bromoiodide and silver chlorobromide.

Photosensitive materials may be spectrally sensitized with the solutions of this invention in any convenient manner, such as by forming a liquid dispersion of the photosensitive material in a hydrophilic colloid, and adding a dye solution of the invention thereto. Dried coatings of photosensitive material, including binderless deposits of silver halide may be sensitized by bathing the coating 6 in dye solutions of the invention. Effective dye concentrations depend on the particular dye and photosensitive material. For silver halide most dyes provide good results at concentrations of about 5 to mg. dye per liter of flowable emulsion.

The solutions of the invention are especially useful in spectrally sensitizing photographic silver halide emulsions. These emulsions may contain the usual addenda such as the chemical sensitizers, stabilizers, speed increasing agents, plasticizers and hardeners, and coating aids referred to in US. Pat. 3,039,873, columns 10-12. The silver halide or other radiation sensitive material may be dis persed in any suitable medium preferably a hydrophilic colloid such as those referred to in column 13 of US. Pat. 3,039,873. The photo-sensitive emulsions or materials spectrally sensitized in accordance with the invention may be coated on any suitable support, such as film base, e.g., cellulose acetate or polyethylene terephthalate, or other supports such as paper, including polyolefin (e.g., polyethylene or polypropylene) coated paper.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

We claim:

1. A highly stable aqueous solution of an acid substituted photographic spectral sensitizing dye having the formula:

wherein R represents a member selected from the group consisting of alkyls having 1 to 4 carbon atoms, sulfoalkyls in which the alkyl group has from 1 to 4 carbon atoms, and carboxyalkyls in which the alkyl group has from 1 to 4 carbon atoms; Z and Z represent the nonmetallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of the benzoxazole series and the naphthoxazole series; D represents an alkylene group having 1 to 4 carbon atoms; and L represents a methine group, said solution having a pH within the range of about 6 to 7.5.

2. The solution of claim 1 wherein said dye is a diacid substituted dye.

3. The solution of claim 2 wherein said diacid substituted dye is soluble in the aqueous solution at the rate of at least .001 part dye per 20 parts water.

4. The solution of claim 3 wherein said dye is a diacid substituted oxacarbocyamine dye.

5. A highly stable solution of anhydro-5,5'-dichloro- 9-ethyl-3,3'di(3-sulfopropyl)oxacarbocyanine hydroxide, sodium salt in water, said solution having the pH adjusted to about 6 to 7.5 with from 10- to 10- moles of pyridine.

References Cited UNITED STATES PATENTS 2,503,776 4/1950 Sprague 260240.65 2,912,329 11/ 1959 Jones et al. 260240.65 3,148,187 9/1964 Heseltine 260240.4

FOREIGN PATENTS 742,112 12/ 1955 Great Britain 2602406 JOHN D. RANDOLPH, Primary Examiner US. Cl. X.R. 

